Synchronous counter system



Sept. 17, 1963 D. w. KERMODE SYNCHRONOUS COUNTER SYSTEM Filed March 13, 1962 United States Patent O 3,104,374 SYNCHRONOUS COUNTER SYSTEM David W. Kerrnode, 107 Arondo Court, Ridgecrest, Calif. Filed Mar. 13, 1962, Ser. No. 179,499 6 Claims. (Cl. 340-168) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of `any royalties thereon or therefor.

This invention relates to telecontrol systems of the type in which a sending counter synchronously controls ia receiving counter by means of a pulsed si-gnal, and more particularly to such a telecontrol system employing magnetron beam switching tubes.

Telecontrol systems of the typ-e referred to oder many advantages over the types of telecontrol systems employing Xed frequency tone signals or linear amplitude vlariation signals. Among these advantages are (l) relative freedom from interference by noise and variation of receiver input signal level due to the inherent reliability of detection `of pulsed signals, (2) simplicity of the accessory equipment for detecting the pulse signals at the receiver, and (3) the considerable flexibility faiiorded -as the result of the almost unlimited number of independent counter states which may be provided by techniques for cascading the counters.

The synchronous counter systems of the prior art have generally been electro-mechanical, employing relays and electromagnetic stepping switches, and have used mechanical switches which operate by the opening land closing of switch contacts. One disadvantage of such prior art systems is their inherent slowness `due to the inertia of the mechanical parts and relative 'slowness off opening and closing mechanical switch contacts. Also the electro-mechanical components are bulky and heavy and in many instances require ,a power supply which is several orders of magnitude larger than the power supply needed for the communication equipment.

Accordingly, an object orf the present invention is to provide a novel and improved telecontrol system of the type employing synchronouslyoperated counters.

Another object is to provide a telecontrol system ott the type employing synchronously operated counters capable of very high speeds of operation.

A further object is to provide a telecontrol system of the type employing synchronous counters capable of operation from communication equipment power supplies.

Other objects, features and many of the attendant advantages of this invention will be readily appreci-ated as the same become better understood by reference to the following detailed description when considered in connection with the accompanyingT drawings wherein:

FIGS. 1A and 1B are ya schematic or a remote radio control system in accordance with the invention;

FIG. 2 is a diagrammatic representation of the physical structure of the magnetron beam switching device of FIGS. 1A and 1B; and

FIG. 3 is a series of curves illustrating waveforms taken at various points in FIG. 1A.

Referring now to the drawing, the invention comprises a telecontrol system employable in various organizations in which :a mechanism is to be controlled and operated at a distance, such as in remote control systems for dirigible vehicles, timing systems for test range instrumentation, and circuit selection systems for dial telephone apparatus or automatic computers. Illustrative oi? one such organi- `zation is ra radio remote control system intended for controlling a target drone (not shown) comprising a sending station 10, FIG. 1A, and a receiving station 12, FIG. 1B.

Sending station comprises a conventional magnetron Ibeam switching tube 14, FIGS. 1A and 2, such :as the 6700 series type tube manufactured by the Burroughs Corporation of Plaineld, NJ. Referring to FIG. 2, tube 14 comprises an evacuated and sealed envelope (not shown) containing a centr-al beam emitting electrode 16. An electron beam 17 may be lformed in any one of a successive series of equiangularly spaced generally radial p0- sitions numbered 0, 1, 2 etc., in the clockwise direction. Ten positions have been illustrated, which is typical of a tube [designed for `decade count-ing. At each position there is `disposed a generally L-shaped electrode 1? commonly known as a target, which serves as an anode to receive the beam 17; a generally U-shaped electrode 20 commonly known -as fa spade, which serves to shape and hold the electron beam; and a beam switching grid 22. A negative voltage applied to the beam switching grid at the position next in series to the existing position oi the beam causes the lbeam to be switched to the target of such next position. Similar voltage variations on grids other than the one next in series to the existing position of the beam do not cause this switching. Beam emitting electrode 16 is connected to vground and the spades 20 and tar-gets 18 are connected to positive direct current (DC.) sources (not shown) to provide operating voltages for the tube. The beam switching grids 22 of the even numbered (including 0) positions are connected to a common conductor 24 while the grids of the odd numbered positions are connected to a different common conductor 26.

Forming the control input of sending station 10 is -a beam reset .and stop control 28 for resetting the beam to its 0" position and limiting subsequent stepping ott the bea-m under successive switching signals to `a selected position, so that the beam will stop at the elected position. Such a control is commonly known as a presefwand is conventional in the art of counter circuits. One type of beam reset and stop control operates by controlling the potentials supplied to the spades and targets of tube 14. For example, the beam may be reset to the 0 position by momentarily depressing the potentials of .all spade electrodes and maintaining the potential of the yspade at the 0 position depressed a iinite time longer than the spades of the other position. Under subsequent switching, the beam may be caused to stop at the selected position by applying operating potentials only to the Ispades and tan gets of the beam positions of the `series extending through the selected position. The beam will simply be prevented from forming at positions subsequent in series to the selected position because of absence oi operating potential, and Iwill therefore remain formed at the selected position. Control Z8 has a suitable preselection input (not shown) by which it may be set to stop the beam 1at the selected position, which input may be adapted for manual operation, as by actuation a preset count .control element, or it may be operated by control circuits which in turn are part of a more comprehensive circuit selection system.

A `source of alternating current (A.C.) such as oscillator 30 produces an A C. signal lwhich is coupled to the primary winding of a transformer 32. The secondary winding 34 of tnansformer 32 has la center tap which is connected to =a tap 36 of a Voltage dividing network located between a positive source and ground. One end of secondary winding 3,4 is connected to conductor 24 and one side of a diode 38, the diode 33 being poled with its cathode connected to the center tap of winding 34. The other end of winding 34 is connected to conductor 2.6 and one side of a diode 40, the Idiode `40 being poled with its cathode connected to the center tap. During the 'half cycle when the end of secondary winding 34 connected to conductor 24 is positive with respect to the other end, diode 38 acts las a short circuit preventing the `application of any pulse signal to the switching grids of the even sets and diode 40 acts as an 3 open circuit permitting a negative pulse to be applied by way of conductor 26 to the switching grids of the odd sets. When the polarity reverses, a negative signal will be applied to switching grids of the even sets and no signal to the switching grid of the odd sets. Thus, negative pulses formed by each half cycle of the signal produced by oscillator 38 will alternately appear on the even and odd beam switching grids tending to successively switch the beam from position to position of the series of beam positions at a swtiching rate equal to twice the frequency of oscillator Sli. The D.C. potential at tap 36 of the Voltage divider provides the operating bias for the lgrids and is applied to the switching grids of the even and odd sets through the respective halves of secondary winding 34. Upon formation of beam 17 at any target 18, a transient deflection signal appears at the target. The deflection signals appearing at target 18 of the "0 position are coupled, by any suitable coupling device, which in its most simplilied form may be coupling capacitor 42, to an output line 44. Similarly, the deection signals at the target electrodes 18 at position "1" through 19" are coupled to a common output line '46, through coupling capacitors 48. If desired, the coupling between the targets and the respective output lines, may be achieved by a pulse transformer in place of capacitors I42 and 48, which would permit better isolation of the signal. Oscillator 30 also drives a frequency doubler G which produces an A.C. signal having twice the frequency of the output of oscillator 3d with a predetermined phase relationship relative thereto. For example, frequency doubler 50 may be synchronously driven to cause -a start of the positive half cycle of the doubled lirequency signa-l to coincide with the start of the positive half cycle of the output of oscillator 3l). The beam reset portion of control -28 is synchronized with the output of oscillator 3i) by means of a pickup coil 52 associated with the primary winding of transformer 32 to cause resetting of the beam to its O position in synchronous relation to the A.C. signal output of the oscillator, with the resetting occurring in predetermined phase relationship with the A.C. signal output of oscillator 30 and the A C. signal output of frequency doubler Si); In the case of the aforementioned exemplary phase relationship of the signals of oscillator 30 and frequency doubler 50, resetting of the beam to its 0 position would be synchronized to coincide with the positive going half cycle of the signal out of oscillator 30 The doubled frequency signal from doubler 50 is applied to -a high speed gating tube S6, such as beam deilection amplifier tube, type NU 2206-SW6, manufactured by National Union Electric Corporation of Bloomington, Illinois. Tube 56 has la beam emitting electrode S8, a control grid 60, a non-symmetrical beam receiving anode 62, and opposed deection plates 64 and 66, the signal from doubler 50 being applied to control grid 60. The deflection signal through output line 44, which occurs when the beam forms at its "0'" position, triggers a wave shaping circuit 68, such as a conventional phantastron circuit, producing a pulse having a duration equal to the period of one full cycle of the doubled frequency signal of the frequency doubler 50. Each deflection signal through output line 46, due to switching of the `beam to successive positions, triggers a wave shaping circuit 70, which is similar to Shaper 68 but produces a pulse having a duration equal to one half the period of one cycle of the doubled frequency. The outputs of shaping circuits 68 and '70 are applied to dellection plates 66 and 64, respectively. Tube 56 acts as a normally closed gate with deflection plates 64 `and y66 forming a pair of gating inputs. When no signal is present on either of the deliection plates the electron beam is directed centrally Y in the tube to anode 62 and no signal appears at the anode. Presence of a signal yat one or the other of the deflection plates deflects the beam from its central position permitting the signal appearing at control grid 68 to be passed to the anode 62. ,The signal output at anode 62 is applied as the modulating signal to a conventional modulation stage 71 of any suitable type providing a scheme for modulating a radio carrier signal in such way that negative and positive inputs provide distinguishable modulation signal compo` nents. The signal components at the output of the modulator 71 are then coupled to a conventional radio transmitter power output 72 and antenna.

Receiving station 12, FIG. 1B, comprises -a magnetron beam switching tube 14a similar to tube 14, the corresponding parts thereof being designated by like reference numerals with the suix letter La operatively associated with tube 14a is a beam reset control 74 for resetting the beam of tube 14a to its 0 position. Beam reset control 74 is similar in structure and operation to the portion of control 28 which ser-ves to reset the beam of tube 14 to 0y detected signal from the demcdulator 78 is of positive polarity the signals at each secondary will have the exemplary instantaneous polarity relationships shown on the drawing. The lower end (as it appears on the drawing) of secondary winding 82 is connected to a tap 86 of a voltage divider located between a positive source and ground, andthe upper end of secondary Winding 82 is connected, through a parallel network consisting of a resistor 88 and a diode $0, to a conductor 92 connected to each beam switching grid 22o of tube 14a. The parallel network of resistor 88 and diode forms a polarity discriminating circuit which passes only negative polarity signals to the beam switching grids. Diode -90 is poled with its cathode connected to the end of winding 82 and resistor 88 has a relatively large value of resistance. When a positive potential is applied to the secondary winding 82, diode 90 is cut off and substantially none of the signal is applied to the grids due to the high resistance '88 in series with winding 82. When a negative. polarity signal appears secondary winding 82, diode 90 short circuits resistor 88 and the signal is applied to the beam switching grids. The upper end of secondary winding 84 is connected to the trigger input of beam reset control 74 and the lower end of winding 84 is connected to ground. A diode 94 is shunt connected -across winding 84 and poled with its cathode connected to the upper end of winding 84 and forms -a polarity discriminating circuit which short circuits positive polarity signals and passes only negative polarity signals to beam reset control 74.

Coupled between each ltarget electrode 18a at beam positions "2 through u9 and the source ofk operating potential for the targets are individual functioning means 96 to be selectively energized by the sending station. Each functioning means 96 independent-ly performs a control operation for the mechanism operated by the telccontroll system. For example, in a remote control system for a dirigible vehicle `such functioning means may be the individual actuators which steer the vehicle, in a timing system for a test range they may be the triggers rto actu-ate instruments at various stations, or in a circuit selection system they may be selector switches for making a desired connection. Each functioning means 96 is adapted to be energized only when the beam is stopped, or otherwise formed in a relatively steady state, at the target to which the functioning means is connected. This adaptation is symbolically shown in the drawing by bypass capacitors 98 vthrough which relatively transient signal inections are passed. However, it is to be understood that in many practical circuits in which the rate of switching the beam is relatively high, the difference between the amount of energy imparted to the target as the beam is stepped across the target by -a continuously applied switching signal Iand the energy imparted to the target when the beam is stopped thereat is of several orders of magnitude and the threshold of operation of the functioning means may itself serve to be selective of whether the beam is formed to the target in a steady state relationship or not. No functioning rneans has been connected to hte target 22a at the 1" position of the /tube for the reason that in the event receiving station 12 would receive lan unwanted signal modulated by a sine wave, the beam 17a of tube'14a would -alternately shift between the targets of the and "1 positions .and could cause the unwanted energization of a functioning means 'at the l position.

` For a better understanding of the operation of the radio control system of FIGS. 1A and 1B, reference is now made -to FIG. 3 wherein the abscissa represents time; curve A the signal at the output of oscillator 30; curve B the signal at the beam switching grids 22 of the even beam positions of tube 14; curve C the signal at the beam switching grids 22 of the odd beam positions of -tube 14; curve D the signal through output line 44; curve E the signal through output lli-ne 46; curve F the signal output of frequency doubler V5t); and Curve G the signal at the output anode 62 of tube 56.

As an example of system operation, suppos-e that it is desired to remotely energize the functioning me-ans 96 connected to the target 18a of position 5 (not shown) of tube 14a in the receiving station. Accordingly, the appropriate preset count control element of co-ntrol 28 is actuated to initiate movement of the beam of tube 14 and limit such movement to position 5; 'actuation of the control element serving to interrupt the reset function of control 28. At a time To the beam reset and stop control 28 effects formation of the beam at the 0 position. Due tosynchronization means 52, time TU coincides with the start of a positive half cycle of both the signal out o-f oscillator 3ft, curve A, and the signal out of frequency doubler 50, curve F. Formation of -the beam a-t the "0 position of tube 14 produces `an inilection signal 10i), curve D, which triggers shaping circuit 68, which in turn produces a pulse 162, shown by broken line superimposed on curve D, of a duration equal -to one full period of double frequency signal, curve F. Application of pulse 102 to deflection plate 66 gates the signal out of frequency doubler 50* for one full cycle, producing a full cycle signal 164, curve G, at output anode 62 of tube 56. Signal 104 is then transmitted vas a modulation component of the radio signal. Upon demodulation in the receiving station 12 the negative half cycle of full cycle signal 104 passes through the polarity discriminating arrangement associ-ated with secondary winding 84 and triggers beam reset control 74 -to reset the beam of tube 14a to its 0 position. It is to be noted that the positive half cycle of full cycle signal 104 is an unwanted signal which could be eli-minated by suitable delay network in wave Shaper 68 or diode network for by-passing it. However, such elimination is not necessary since the unwanted positive half cycle causes no more than a highly transistory switching of the beam to the l position of tube 14a, which in any case precedes the reset action. The inherent inertia of control 28 may cause the beam to remain at the 0 position of the tube 14 for a finite time. At the conclusion of such finite time, at some moment T1, the negative half cycles pulses alternately applied to the even and odd beam switching grids 22, curves B and C, will cause the beam to step to the position 5 where the beam stops by reason of beam reset and stop control 28. Stepping of the beam causes a series of intiection signals 106, curve E, through output line 46, which trigger shaper circuit 70 to in turn produce a series of pulses 108, shown by broken line superimposed on curve E, each pulse 1018 having a duration equal to one half cycle period of the doubled frequency signal, curve F. Due to synchronization the pulses 1-0-8` are applied to deflection-plate 6d only during the positive hal-f cycle of the4 double frequency signal, resulting'in a train of posi-tive pulses 110,

curve G, at anode 62 of tube 56. Pulses 110"`are trans- 1 mitted and subsequently -received and demodulated` in means 96. It is to be understood that the speed at which?VV the described operation-s take place is limited'only'by the maximum frequency of switching of the beam of tubey 14 which is in thelmegacycle range, so that the entire described operation may take place in several microsec-VV onds or less. A

It will be apparent, from the aforesaid description of operation that the output of frequency doubler 50,' curve F, is in effect a carrier signal which is'modula'ted by the' gating inputs to deflection plates 64 and 66 to produce the positive and negative half cycle positive .pulses at anode 62. It has been foundthat satisfactory resul-ts mayl be obtained with the ,omission of modulation stage 721` in the sending station and demodulation stage 78 in the receiving station. In such case, the output of anode 62 is coupled directly to transmitter output 72, and .fthe

.output of receiver front end 76'is coupled to the primary winding of transformer 80. The doubled frequency signal, curve V(F, then becomes the radio carrier frequency.'

As an example of such operation, satisfactory resultsV without modulation and demodulation stages 71 and 78 have been obtained at radio frequencies from 30 kilo-;. cycles to 2 megacycles using a conventional tuned radio frequency type receiver as front end 76.

Obviously many modilications and variations of the presentinvention are possible in the light of the above teachings; It is therefore to be understood that Within the scope of the appended claims the invention may ybe practiced otherwise than asv specificallyY described. i

What is claimed is: i' l. Remotely controlled counting apparatus comprising, -a sending counter and a receiving counter, each of said counters adapted to be switched from a reference count condition through a series of successive count conditions in step by step response to each pulse of a train of pulses applied to the input thereof, each of said counters having an associated reset means -actuable to switch the counter to its reference counting condition, said sending counter having an individual counter output associated with each count condition and upon assuming a count condition adapted to provide a count signal at the associated output, said sending counter including control means for stopping the [counter at a desired count condition, a lirst source for producing a lirst A.C. signal, circuit means for deriving a train of pulse signals for switching the sendingcounter from said first A.C. signal, each pulse of said series of pulses corresponding to a half cycle of said first A.C. signal, circuit means for deriving a second A.C. signal from said rst A.C. signal, said second A.C. signal (having twice the frequency of said first A.C. signal and having a predetermined phase relationship to said first A.C. signal, normally closed gating means having a signal input, a signal output, and first and second gate inputs, said second A.C. signal being applied to said signal input, tirst signal shaping means interconnecting the output of the sending counter associated with the reference count condition thereof and the first gate input, said irst signal shaping means being adapted to gate a half cycle of said second A.C. signal of one of opposite polarities to provide a reset signal to switch the receiving counter to its reference condition, a second signal shaping means interconnecting the outputs of the sending counter associated with the count conditions thereof subsequent to the reference condition and the second gate input, said second signal shaping means adapted to gate a half cycle of said second A.C.

Veachpulse signal appearing at the aforesaid outputs to provide a count signal to switch-the receiving counter to thecount condition thereof corresponding to the count at which the sending counter is stopped, said receiving count-V er 'having operatively associated therewith polarity discrimination means to actuate the reset meansvof the receiving counter in response to said reset signal and -count signal to the input thereof,and communication circuit means'cronnecting the output of the gating means and the polarity` discrimination means.

2.v Apparatus in accordance with claim l, said sending counter comprising an electronic beam switching device having a beam emitting electrode and a sequential series of beam receiving electrodes, each beam receiving electrode having an individual switching electrode associated therewith for shifting the beam thereto from the preceding beam receiving electrode of the series, the switching electrodes associated with the beam receiving electrodesV of the series forming the inputv of the sending counter, said 'beam receiving electrodes each forming a counter output with the signal intiect thereat upon the beam being switched thereto providing the count signal.

3. Apparatus in accordance with claim 2, said reset means efecting formation of theibeam at the rst beam receiving electrode of the series, said circuit means for deriving a train 'of pulse signals for switching the sending counter being adapted to apply only one of two successive pulses to the beam switching electrode associated with the first beam receiving electrode and only the other of the two successive pulses to the beam switching electrode associated with the second beam receiving electrode.

4. Apparatus in accordance with claim 1, said communication circuit being of the radio type including a radio transmitter having means for modulating a radio carrier signal in accordance with the output of said first means for modulating, and a radio receiver having means for demodulating the receivedradio signal coupled to the input of the polarity discrimination means.

V5. Apparatus in accordance with *claim* 1,'-said cornmunication circuitY being of the radio type including a radio transmitter having output means for transmitting v a radio signal at the frequency of said second signal, said output of the gating means being connected directly to said output means, and a radio receiver having a frequency selective circuit tuned to the frequency oifsaidA second A.C. signal, the output of said frequency selective circuit being directly coupled/to said discriminator means. v

6. A telecontrolY system for selectively energizing one of a plurality of functioning means, comprising; a receiving station including a magnetron beam Yswitchingtube having` a beam emitting electrode, a series of beam re.- ceiving electrodes disposed ina successiveA series, and means actuable to form an electron -beam between said beam` emittingelectrode and the irst beam receiving electrode of said series,..a plurality. of functioning means each individually connected to a diterent beam receiving electrode and energizable in response to formation of a steady state electron beam to the associated beam rel ceiving electrode, each -beam receiving electrode having an individual switching electrode associated therewith for shifting the beam thereto from the preceding beam receiving electrode, a transmitting station including means for generating a first reset signal to -actuate said meansV electrodes of the magnetron'beam switching tube inv such manner that the beam is successively shifted through the intermediate beam receiving electrode positions to the beam receiving electrode associated with the desired functioning means in step with the pulses of the pulse train.

No references cited.`

Aslan- 1 

1. REMOTELY CONTROLLED COUNTING APPARATUS COMPRISING, A SENDING COUNTER AND A RECEIVING COUNTER, EACH OF SAID COUNTERS ADAPTED TO BE SWITCHED FROM A REFERENCE COUNT CONDITION THROUGH A SERIES OF SUCCESSIVE COUNT CONDITIONS IN STEP BY STEP RESPONSE TO EACH PULSE OF A TRAIN OF PULSES APPLIED TO THE INPUT THEREOF, EACH OF SAID COUNTERS HAVING AN ASSOCIATED RESET MEANS ACTUABLE TO SWITCH THE COUNTER TO ITS REFERENCE COUNTING CONDITION, SAID SENDING COUNTER HAVING AN INDIVIDUAL COUNTER OUTPUT ASSOCIATED WITH EACH COUNT CONDITION AND UPON ASSUMING A COUNT CONDITION ADAPTED TO PROVIDE A COUNT SIGNAL AT THE ASSOCIATED OUTPUT, SAID SENDING COUNTER INCLUDING CONTROL MEANS FOR STOPPING THE COUNTER AT A DESIRED COUNT CONDITION, A FIRST SOURCE FOR PRODUCING A FIRST A.C. SIGNAL, CIRCUIT MEANS FOR DERIVING A TRAIN OF PULSE SIGNALS FOR SWITCHING THE SENDING COUNTER FROM SAID FIRST A.C. SIGNAL, EACH PULSE OF SAID SERIES OF PULSES CORRESPONDING TO A HALF CYCLE OF SAID FIRST A.C. SIGNAL, CIRCUIT MEANS FOR DERIVING A SECOND A.C. SIGNAL FROM SAID FIRST A.C. SIGNAL, SAID SECOND A.C. SIGNAL HAVING TWICE THE FREQUENCY OF SAID FIRST A.C. SIGNAL AND HAVING A PREDETERMINED PHASE RELATIONSHIP TO SAID FIRST A.C. SIGNAL, NORMALLY CLOSED GATING MEANS HAVING A SIGNAL INPUT, A SIGNAL OUTPUT, AND FIRST AND SECOND GATE INPUTS, SAID SECOND A.C. SIGNAL BEING APPLIED TO SAID SIGNAL INPUT, FIRST SIGNAL SHAPING MEANS INTERCONNECTING THE OUTPUT OF THE SENDING COUNTER ASSOCIATED WITH THE REFERENCE COUNT CONDITION THEREOF AND THE FIRST GATE INPUT, SAID FIRST SIGNAL SHAPING MEANS BEING ADAPTED TO GATE A HALF CYCLE OF SAID SECOND A.C. SIGNAL OF ONE OF OPPOSITE POLARITIES TO PROVIDE A RESET SIGNAL TO SWITCH THE RECEIVING COUNTER TO ITS REFERENCE CONDITION, A SECOND SIGNAL SHAPING MEANS INTERCONNECTING THE OUTPUTS OF THE SENDING COUNTER ASSOCIATED WITH THE COUNT CONDITIONS THEREOF SUBSEQUENT TO THE REFERENCE CONDITION AND THE SECOND GATE INPUT, SAID SECOND SIGNAL SHAPING MEANS ADAPTED TO GATE A HALF CYCLE OF SAID SECOND A.C. SIGNAL OF THE OTHER OF OPPOSITE POLARITIES IN RESPONSE TO EACH PULSE SIGNAL APPEARING AT THE AFORESAID OUTPUTS TO PROVIDE A COUNT SIGNAL TO SWITCH THE RECEIVING COUNTER TO THE COUNT CONDITION THEREOF CORRESPONDING TO THE COUNT AT WHICH THE SENDING COUNTER IS STOPPED, SAID RECEIVING COUNTER HAVING OPERATIVELY ASSOCIATED THEREWITH POLARITY DISCRIMINATION MEANS TO ACTUATE THE RESET MEANS OF THE RECEIVING COUNTER IN RESPONSE TO SAID RESET SIGNAL AND COUNT SIGNAL TO THE INPUT THEREOF, AND COMMUNICATION CIRCUIT MEANS CONNECTING THE OUTPUT OF THE GATING MEANS AND THE POLARITY DISCRIMINATION MEANS. 